1. Field of the Invention
The present invention relates to a method for measuring a free-state diameter of a metal ring of a metal belt for a continuously variable transmission by cutting the metal ring.
2. Description of the Related Art
A metal belt used in a continuously variable transmission typically includes a plurality of metal elements mounted on metal ring assemblies, each metal ring assembly having a plurality of metal rings laminated on one another. Accordingly, a driving force is transmitted by a pushing force between the metal elements, which are in contact with one another, in a state in which the metal belt has been reeved around a driving pulley and a driven pulley. A stress applied to each of the metal rings supporting the metal elements in the metal belt is varied periodically during traveling of the metal belt along the driving pulley and the driven pulley. Moreover, the applied stress is different between an inner peripheral surface and an outer peripheral surface of the metal ring. If the stress applied to the inner peripheral surface of the metal ring and the stress applied to the outer peripheral surface are not uniform, a face of the metal ring which receives a large stress fatigues early, which causes a reduction in the overall fatigue life of the overall metal ring assembly.
Conventional metal belts are disclosed in Japanese Patent Application Laid-open No. 63-20945 and Japanese Patent Publication No. 7-110390, wherein a residual stress is pre-applied to each metal ring so the stresses applied to the inner and outer peripheral surfaces of the metal ring are as uniform as possible. Thus, any stress generated by the operation of a continuously variable transmission is countervailed by the residual stress and the fatigue life of the metal ring is prolonged.
In the conventionally known metal belt, in order to verify whether the magnitude of the residual stress applied to the metal ring is equal to a preset value, the metal ring is cut at one point to provide a state (a free state) in which a sum of moments generated by the residual stress is zero, and the diameter of the metal ring in the free state is measured. If the residual stress applied to the metal ring is a tensile stress on the outer peripheral surface and a compression stress on the inner peripheral surface, cut ends formed upon cutting of the metal ring are moved away from each other, and the diameter in the free state is larger than that in the endless state (a non-cut state). However, if the residual stress applied to the metal ring is a compression stress on the outer peripheral surface and a tensile stress on the inner peripheral surface, cut ends formed upon cutting of the metal ring are moved toward each other to interfere with each other as shown in FIG. 10B, and for this reason, the free-state diameter 2Ro (see FIG. 10G) cannot be measured accurately.
Accordingly, it is an object of the present invention to ensure that the free-state diameter of each of the metal rings of the continuously variable transmission can be measured accurately.
To achieve the above object, according to a feature of the present invention, there is provided a method for measuring a free-state diameter of each of metal rings of a metal belt for a continuously variable transmission by cutting the metal ring, the free-state diameter of the metal ring being determined so that a predetermined compression stress and a predetermined tensile stress are applied to an outer peripheral surface and an inner peripheral surface of the metal ring in an endless state, respectively, wherein the metal ring is cut at least at two points so that cut ends formed upon cutting of the metal ring do not interfere with each other in a free state, and a free-state diameter is measured.
With the above configuration, the free-state diameter of the metal ring being determined so that the predetermined compression stress and the predetermined tensile stress are respectively applied to the outer peripheral surface and the inner peripheral surface of the metal ring in the endless state. Therefore, if the metal ring is cut at one point in order to measure the free-state diameter, the cut ends interfere with each other, but the interference can be avoided by cutting the metal ring at two points to measure the free-state diameter, whereby accurate measurement can be achieved.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.